Method for preparation of cationic cellulose

ABSTRACT

The invention is a fibrous, cationic cellulose pulp product and the method for preparing it. A water suspension of cellulosic fiber is treated under alkaline conditions with a condensate of epichlorohydrin and dimethylamine. Up to 30 molar percent of the DMA may be replaced by a crosslinking agent such as ammonia or a lower aliphatic diamine. The process may be carried out at room or elevated temperatures. It is practical to add the condensate at one of the later alkaline stages of a bleaching process; e.g., an alkaline extraction or peroxide stage. This is most preferably done later than any chlorination or hypochlorite stages. The product shows greatly improved retention of acid and other anionic dyes. It also shows superior retention of some pigments and latices without the need for other cationic aids. In some cases a small amount of alum appears to have a synergistic retention effect with the cationic pulp product when used with titanium dioxide and certain anionic latices.

BACKGROUND OF THE INVENTION

The present invention is a fibrous, cationic cellulose pulp product andthe method for preparing it. The product is especially advantageous inpapermaking for its improved retention of certain dyestuffs and fillermaterials.

The surface of cellulose fibers is normally slightly anionic in naturedue to the presence of carboxyl and carbonyl groups introduced duringthe pulping and bleaching process. This negative charge is responsiblefor a number of undesirable effects in papermaking. Principal amongthese is the tendency of the longer fibers to repel fine celluloseparticles which result from refining and the similar tendency to repelmany additives such as fillers, pigments, dyes, and sizes, many of whichalso bear negative charges. As a result, these fine particles tend to gointo the white water during sheeting where they represent an economicloss and a pollution problem. In response to this problem, alum hastraditionally been added to adjust the electrical charge of surfaces towhich it is adsorbed. However, alum is not very efficient; therefore,relatively large amounts are required. This produces an undesirable,relatively highly acidic environment both in the sheeting process and inthe final paper product. In the papermaking process, this acidity tendsto corrode equipment. In paper it results in relatively rapid loss ofphysical properties such as tear strength and fold resistance.

A number of routes have been explored using materials besides alum toovercome the anionic nature of cellulose fibers. One such route, whichhas seen commercial use for approximately 30 years, has been the use ofadditives which are cationic in nature; e.g., cationic starch. Theseadditives are attracted to the anionic cellulose and serve to modify orneutralize the electrical charge so that the fibers have less tendencyto repel anionic additives. Today a relatively wide variety of cationicpapermaking additives are available. These include materials forimproving drainage rate, reducing fines and pigment loss, and increasingwet strength. Cationic additives also make the use of less acidic sizingagents possible. Alkyl ketene dimers are such a sizing agent applied inthe pH range of 6-8. Articles to McKenzie, Appita 21(4): 104-116 (1968)and to Moore, Tappi 58:99-101 (1975) are informative of the state of theart.

Another route to overcoming the anionic nature of cellulose fibers hasreceived considerable research although no products have yet evolvedwhich have been of commercial importance. This approach has been to makethe fibers themselves cationic in nature, usually by reaction with amaterial that introduces positively charged nitrogen atoms into asubstituent side chain. Uwatoko, Kagaku Kogyo (Japan) 25 (3):360-362(1974) briefly summarizes the state of the art in regard to cationicfibers. Uwatoko lists six major approaches that have been taken. Withoutputting them in any chronological order, these are as follows: the firstmethod introduces side chains containing a tertiary nitrogen atom. Theseside chains are attached to the cellulose molecule at the hydroxylgroups as ethers. One product of this type which has receivedconsiderable study is the quaternized diethylaminoethyl derivative ofcellulose. A second route to the preparation of cationic cellulose isthe reaction of cellulose in the presence of sodium hydroxide withethanolamine, aqueous ammonia or melamine. A third process is thereaction between cellulose and a material such as 2-aminoethyl sulfuricacid in the presence of sodium hydroxide. Another product has beenformed by iminating an aminated cellulose by reaction between theaminated cellulose and ethylene imine. An approach which has receivedconsiderable study is the reaction of various trimethyl ammonium salts.Of particular importance has been glycidyl trimethyl ammonium chloridereacted with cellulose in the presence of a catalytic amount of sodiumhydroxide. A related approach has been the reaction of2-chloroethyldiethyl amine with alkali cellulose. This product is thenquaternized with methyl iodide in anhydrous alcohol. Finally, Uwatokodescribes a modified cellulose described in more detail in J. Soc. FiberSci. Technol. (Japan) 30 (5/6):T313-314 (1974). In this processcellulose is reacted with a solution of sodium acid cyanamid at aconcentration of 50-200 g/L at a pH in the range of 10-13 andtemperature of 10°-40° C. for 4-24 hours.

One approach not specifically discussed by Uwatoko is the reaction ofcellulose with a mixture of epichlorohydrin and a tertiary amine withcellulose in the presence of aqueous sodium hydroxide. This process isdiscussed by McKelvey and Benerito in J. Appl. Polymer Sci. 11:1693-1701(1967). Paschall, in U.S. Pat. No. 2,876,217 describes the use of thisprocess to make a granular cationic starch useful as a papermakingadditive. Benerito et al., Anal. Chem. 37:1693-1699 (1965) describe indetail the production of quaternary ammonium ethers of cellulose by thereaction of diethylaminoethyl cellulose with either methyl iodide orethyl bromide under completely anhydrous conditions.

Kaufer et al., Papier (Darmstadt) 34(12):575-579 (1980) describesseveral applications of cellulose made cationic by the reaction ofglycidyl trimethyl ammonium salts. These authors also teach theusefulness of β-methacryloxyethyltrimethyl ammonium chloride as acationizing agent.

Krause et al., Papier (Darmstadt) 35(IOA):33-38 (1981) building on thework of Kaufer and his coworkers, show the superiority of cationic pulpsin retaining alkyl ketene dimer sizing materials as opposed to theconventional use of cationic starches as retention aids.

In West German Pat. No. 2,817,262, John et al. show that only part ofthe fiber in a papermaking stock needs to be cationized in order toachieve significant benefit.

Stone et al., in Canadian Pat. No. 838,684 teach the preparation of awide variety of quaternary nitrogen-containing cellulose ethers whichfunction as cationic materials.

Lewis et al., in U.S. Pat. No. 3,694,393 show the treatment of cellulosewith the reaction product of epichlorohydrin and dimethylaminoethylmethacrylate.

There appear to be a number of reasons why a cellulose pulp havingcationic substituents has never appeared commercially in the marketplaceas a papermaking fiber. One of the principal reasons is the expense. Inmany cases the raw materials themselves are very expensive. Along withthis is the problem that the reaction conditions of the cellulose withthe substituent materials are such as to cause the cost of the productto be greatly elevated. Many of the cationic cellulose materialsproduced by straightforward chemical reaction are not of fibrous nature.This is a problem with relegates them to the nature of an additive inpapermaking as opposed to use as a primary fiber. A number of theproducts which are fibrous must be produced by grafting reactions. Herefree radical sites are induced in the cellulose chains by means such asceric ion activation or high energy irradiation. An appropriatepolymerizable monomer having vinyl unsaturation is then coupled to thecellulose and polymerized in the presence of a free radical initiator.The overall result has been a group of products which are eithertechnically unsuitable or far too expensive for general use.

Cationic starches, which have been available commercially for over 30years, do have some relationship to the cationic celluloses justdescribed. One who sits on the edge of this particular scientific artmight question why the processes used for the preparation of cationicstarches have not successfully been applied to cellulose fibers. Thereis a ready answer. In the first place, most of the cationic starches aremodified in physical nature by cooking or partially cooking during thechemical reaction which introduces cationic sites. There is not any needfor these products to retain their original physical form. A secondreason is that cationic starches are used in relatively smallpercentages in papermaking. Therefore, they form only a small portion ofthe ultimate product. This fact makes their relatively high costs moretolerable to the papermaker. While there is no need to review all of theextensive technical literature relating to cationic starches, a fewrecent patents bear some relationship to the present invention. Aitken,U.S. Pat. No. 3,674,725 describes a product in which apolyepichlorohydrin is modified with an amine, preferablytrimethylamine. This product can then be reacted with a starch understrongly alkaline conditions. The same inventor, in U.S. Pat. Nos.3,854,970 and 3,930,877 teaches an approximately equal molar compositionof epichlorohydrin and dimethylamine reacted under alkaline conditionsand then acidified to produce a quaternary ammonium salt. The preferredcompositions have 10-20% ammonia substituted for an equivalent of thedimethylamine. These condensates can be used to prepare liquid cationicstarches by reaction under rather strongly alkaline conditions withpartially hydrolyzed starches. Buikema, U.S. Pat. No. 4,029,885, showsthe use of those starches for sizing paper. Buikema et al., U.S. Pat.No. 4,146,515 treat a lightly oxidized starch with anepichlorohydrin-dimethylamine condensate at about 60°-80° C. for onehour. This product is subsequently acidified to make an amine salt.Cosper et al., U.S. Pat. No. 4,268,532, use adimethylamine-epichlorohydrin polymer with a second polymer (which mayor may not be anionic) for retaining starch in repulped broke. It isinteresting that these inventors do not appear to have considered thepossibility of reacting their epichlorohydrin-dimethylamine condensatewith cellulose to produce a product which could be both fibrous andcationic in nature.

The present invention describes a cationic cellulose made by reaction,under mildly alkaline aqueous conditions, of cellulose fibers with oneof a group of condensates based on the reaction product ofepichlorohydrin and dimethylamine. The reaction conditions and nature ofthe materials involved is such that a fibrous product results which alittle more expensive to manufacture than the cellulose itself.

SUMMARY OF THE INVENTION

The present invention is a fibrous cationic cellulose product and aprocess for making it which comprises an additive of cellulose with amaterial which is either a condensate of epichlorohydrin anddimethylamine or a condensate of this type which has been furthermodified by replacing a portion of the dimethylamine with across-linking agent which may be ammonia or a primary aliphatic diamineof the type H₂ N--R--NH₂, where R is an alkylene radical having from twoto eight carbon atoms.

The proportions of epichlorohydrin and dimethylamine may vary within therange of about 0.8 to 3 moles of epichlorohydrin for each mole ofdimethylamine. The preferred condensates will be approximately equalmolar in proportion. Ammonia and the primary aliphatic diamines serve toact as cross-linking agents for the additive condensates. Further, theiruse increases the number of tertiary nitrogen atoms which may bequaternized to provide sites for positive charges. Up to 30 molarpercent of the dimethylamine may be replaced by ammonia or the aliphaticdiamine in the condensation process. In general, it is preferred thatthe molar percentage of ammonia or aliphatic diamine be in the range of10-20%. Preparation of condensates suitable for use in the presentinvention is described in U.S. Pat. No. 3,930,877 to Aitken.

It should be considered within the scope of the invention to usemixtures of any of the above condensates.

While the cationic cellulose product of the present invention isdescribed as an "additive" of cellulose with theepichlorohydrindimethylamine condensate, it will be understood by thoseskilled in the art that the condensate may be covalently bonded to thecellulose by virtue of pendant epoxy moieties which react byetherification with the hydroxyl groups on the cellulose molecules.Alternatively, the condensates may be hydrogen bonded or otherwiseattached to the cellulose. In all probability both mechanisms arepresent.

Among the modifying agents which serves as potential cross linkers forthe condensate, ethylene diamine and hexamethylene diamine are preferredmaterials.

The additive material may be used effectively in relatively highamounts. Typically usage will be in the range of 0.5-20 kg/t (1-40lbs/t). The preferred range of usage is about 1-10 kg/t. These usagesare somewhat nominal and are based on manufacturer specified solidspercentages in the aqueous solutions of condensates sold commercially.These solids percentages are only appropriate for activeepichlorohydrindimethylamine condensate since they are based on rawmaterials charged to the synthesis reactor. This approximation procedureis necessary because of the great difficulties in analyzing thecondensate solutions without inducing decomposition of the product. Insubsequent examples, calculations will assume that the percent solids asspecified by the condensate manufacturer are equivalent to percentactive epichlorohydrin-dimethylamine condensate.

One of the unique aspects of the present invention is the method ofmaking the cationic cellulose product. It has been discovered againstall expectations that it is only necessary to add an aqueous solution ofthe additive to a suspension of cellulose in water which has had the pHraised into the alkaline range, preferably to the range of approximately10.0-10.5, and to agitate this mixture for 30 minutes or less at room orelevated temperature. Most surprisingly, the process may be carried outat an alkaline stage in the bleaching process, preferably after anyhypochlorite treatments, whereupon the resulting additive appearsresistant to further bleaching operations. In the usual bleachingschedule for a kraft pulp, the condensate is conveniently added duringan alkaline extraction stage or hydrogen peroxide stage during thelatter part of the bleaching sequence. In this way, no changes in thebleaching sequence are necessary nor are any additional steps requiredto produce the cationic additive. This discovery flies in the face ofexpectations that the oxidizing environment in bleaching stages duringor following the addition of the condensate would either remove it ordestroy its effectiveness.

It is thus an object of the present invention to provide a fibrouscellulosic product which is cationic in nature.

It is another object of the invention to provide a cationic celluloseproduct with improved effectiveness in retaining anionic papermakingadditives.

It is a further object to provide a cationic cellulose which hasextremely high retentivity of acid dyes.

It is another object of the invention to provide a simple andinexpensive process for the preparation of a fibrous cationic celluloseproduct.

It is still another object to provide a process for the manufacture of acationic cellulose product which can be carried out during an alkalinebleaching stage and which does not require a separate process step.

These and many other objects will become readily apparent to one skilledin the art upon reading the following detailed description of theinvention taken in conjunction with the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the point in thebleach sequence at which the cationic additive was combined with thecellulose and the color intensity of the dyed product.

FIGS. 2 and 3 are graphs showing the color intensity versus the amountof dye used for a family of cationic cellulose products having differentamounts of additive.

FIG. 4 is a graph showing the amount of titanium dioxide retained versusthat added for a family of cationic cellulose products treated withdifferent amounts of additive.

FIG. 5 shows opacity of the ultimate paper products plotted against theamount of titanium dioxide added to a family of cationic celluloseproducts having different amounts of additive.

FIGS. 6 and 7 are graphs similar to FIGS. 4 and 5 but in which adifferent cationic additive was used.

FIGS. 8 and 9 are graphs showing the effectiveness of cellulose fiberstreated with various amounts of cationic additive in adsorbing an aciddye from an aqueous solution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The cationic cellulose product of the present invention is readilyprepared by adjusting the pH of a water slurry of cellulose to a pHwhich is preferably about 10.5 and then adding the desired amount of anaqueous solution of the epichlorohydrin-dimethylamine (Epi-DMA)condensation product. Temperature is not critical. The system worksequally well at room or elevated temperatures. The slurry is agitatedfor about 10-30 minutes whereupon the resulting treated pulp is drainedand washed. From this point it may either be sheeted or sent in the wetstate for further processing. It is surprising and totally unexpectedthat a cationic cellulose product could be made under the mildconditions outlined above. This is especially so in view of the harsh(5% alkali and near boiling temperatures) outlined in U.S. Pat. No.3,854,970 for preparation of cationic starches from Epi-DMA condensationproducts similar to those used in the present invention.

What is also surprising and unexpected about the process alternativesfor making the cationic cellulose product is that the Epi-DMAcondensation product can be added at any later alkaline stage of a pulpbleaching sequence where the pH is preferably about 10 or higher. Thestage at which the condensate is added should preferably be later in thebleach sequence than any hypochlorite stage. The presence of highlyoxidizing conditions in the stage at which the condensation product isadded, or in subsequent bleaching stages, appears to make little or nodifference. It also makes no difference whether the bleaching stage isone carried out at ambient or elevated temperatures.

The discovery that the Epi-DMA condensation product may be added duringan alkaline bleaching step is of great importance to the processeconomics. For the first time it enables a cationic cellulose product tobe made without any additional process steps over those normallyrequired for making a bleached fiber. The only process expense is thecost of the condensation product. In the present case these products arearticles of commerce made from readily available and relativelyinexpensive commodity chemicals. They are used only in modest amounts inthe range of 0.5-20 kg/t. Process efficiency, in terms of condensationproduct which actually bonds to the cellulose, ranges from essentially100% at the low end of usage to over 80% at high end.

The following examples give detailed instructions on the best mode knownto the inventors of making and using the products of the invention.

EXAMPLE 1

Bleached, spruce kraft pulp (Sample 1) was obtained from a pulp mill.Samples having 15.5 g of dry fiber were slurried in water at 2%consistency (759.5 g total water). The pH was adjusted to 10.5 with NaOHand 0.31 g of a 50% solution (10 kg/t on an active material basis) of anunmodified Epi-DMA condensate (Nalco N-7655 Nalco Chemical Co., OakBrook, Ill.) was added to the slurry. Temperature of the slurry was20°-23° C. After agitation for about 30 minutes, the slurry was dilutedto about 0.5% consistency and a handsheet was made. The sample was notwashed other than by dilution during sheeting. Kjeldahl nitrogen contentof the treated pulp (Sample 2) was 0.046% indicating an add-on of 8.7kg/t and a retention efficiency of about 87%. Nitrogen content of thecondensate was measured as 5.3% on an as received (50%) basis. Theuntreated pulp control had a nitrogen content of less than 0.001 %.

EXAMPLE 2

A sample of partially bleached Douglas-fir kraft pulp was taken from thebleach plant of a pulp mill after the third of a five or six-step bleachsequence. The normal mill bleach sequence consists of a first stagechlorination using 75 kg/t Cl₂ for about 30 minutes at a temperature ofabout 32° C. At the end of the bleach stage the pH is approximately 1.8.

After washing following the chlorination, the pulp was given a treatmentusing about 37.5 kg/t NaOH and about 15 kg/t sodium hypochlorite at a pHin the range of 10-11 and temperature in the 60°-71° C. range for aboutone hour. While this is usually referred to as a "neutral hypochlorite"stage, it is essentially an alkaline extraction step with hypochloritebeing present.

Following washing after the alkaline hypochlorite treatment, the pulpwas given a hypochlorite bleach using 15 kg/t sodium hypochlorite atabout 40° C. for approximately one hour. The pH toward the end of thestep was maintained at a level slightly above 9 by the addition ofcaustic as necessary.

While the pulp samples for laboratory treatment were taken on thewashers following the hypochlorite step, the rest of the steps in anormal mill sequence will be described here.

Alkaline extraction follows next, using about 10 kg/t NaOH at 60°-71° C.for about 30-60 minutes. The pH in this treatment is about 10.5 makingit an ideal point in a plant bleach sequence for the addition of theEpi-DMA condensate product to the pulp.

After washing following extraction, the pulp is given a chlorine dioxidetreatment using about 7.5 kg/t ClO₂ with about 2 kg/t NaOH added laterin the step for pH control. The pH at the end of the treatment will beabout 3.5. This is a hot treatment with temperatures usually in the65°-82° C. range, typically about 70° C. The time will vary between 30minutes and 31/2 hours although 1/2 to 1 hour is most common.

For many pulp products the chlorine dioxide stage is the final bleachtreatment. If a customer wishes a whiter product, from 2-4 pointsadditional brightness can be gained by using a peroxide treatmentfollowing the chlorine dioxide stage. This was about 1.5 kg/t ofhydrogen peroxide at about 71° C. with the pH raised by NaOH to about10.5. Again, time is variable ranging from 30 minutes to 6 hours, moretypically about 1 hour.

While a detailed description of various pulp bleaching sequences is notof importance to the present invention, the reader wishing more detailcan refer to several standard pulping texts and to U.S. Pat. Nos.4,303,470 (Meredith, et al.) and 4,298,426 (Torregrossa, et al.).

Using the pulp samples taken in the pulp mill after the hypochloritestage, a series of samples was made in which two additional bleachingstages were completed in the laboratory. Epi-DMA condensate (Nalco 7655)was added at the alkaline extraction step. In each bleach trial 30 g ofO.D. pulp was used. The following table shows the conditions and resultsof the trials.

                  TABLE I                                                         ______________________________________                                        Laboratory Final Stage Bleaching                                              Sample No.          3       4                                                 ______________________________________                                        Extraction Stage                                                              NaOH, %             0.9     0.9                                               .sup.(1) Epi-DMA, % --      1.0                                               Time, min.          45      45                                                Temp. °C.    70      70                                                Initial pH          12.4    12.45                                             Final pH            11.9    11.75                                             Chlorine Dioxide Stage                                                        ClO.sub.2, %        0.85    0.85                                              NaOH, %             0.34    0.34                                              Time, min.          180     180                                               Temp, °C.    70      70                                                Final pH            3.3     3.1                                               Properties                                                                    Kjeldahl N, %       <0.001  0.041                                             .sup.(2) Epi-DMA Retention, %                                                                     --      78                                                .sup.(3) Dye Intensity, L Value                                                                   91.4    69.5                                              ______________________________________                                         .sup.(1) Nalco 7655. Calculated on active material basis. All percentages     are based on pulp.                                                            .sup.(2) Retention as % of material charged.                                  .sup.(3) Based on treatment in aqueous slurry with 1% Amafast Turquoise       8GPB dye. (CibaGeigy, Greensboro, North Carolina). Color intensity            expressed as "L Value" on Hunter Colorimeter. Lower values indicate more      intense color.                                                           

EXAMPLE 3

Another bleached pulp sample was taken from the pulp mill bleach plantfollowing the chlorine dioxide stage but prior to a hydrogen peroxidetreatment. The peroxide stage was completed in the laboratory in similarfashion to the bleaching done in Example 2. The following table showsconditions and results.

                  TABLE II                                                        ______________________________________                                        Sample No.          5       6                                                 ______________________________________                                        Extraction Stage                                                              H.sub.2 O.sub.2, %  0.12    0.12                                              NaOH, %             0.10    0.10                                              Na Silicate, %      0.6     0.6                                               .sup.(1) Epi-DMA, % --      1.0                                               Time, min.          150     150                                               Temp. °C.    65      65                                                Initial pH          10.5    10.3                                              Final pH            10.3    10.0                                              Properties                                                                    Kjeldahl N, %       <0.001  0.044                                             .sup.(2) Epi-DMA Retention, %                                                                     --      83                                                .sup.(3) Dye Intensity, % dye                                                                     91.9    70.2                                              ______________________________________                                         Please refer to Table I for footnotes.                                   

EXAMPLE 4

Dyeing tests were made on the product of Sample Nos. 1, 2, 4 and 6 ofExamples 1-3. Sample 1 is an untreated fully bleached kraft pulp. Sample2 is a fully bleached pulp treated with 10 kg/t of Epi-DMA condensate.Sample 4 had 10 kg/t of Epi-DMA added at the caustic extraction stageprior to the chlorine dioxide stage. Sample 6 had 10 kg/t of Epi-DMAadded at the final peroxide bleach stage.

In order to study dye retentivity of the cationic cellulose product, 5 gdry weight of pulp was slurried at 1% consistency in room temperaturetap water and run for two minutes in a high shear blender. The dye wasadded and mixing was continued as necessary to disperse the dye in orderto simulate light refining. Handsheets were made of the dyed fiber andcolor intensity was then measured on a Hunter Colorimeter, Type D-25A(Hunter Laboratories, Research Triangle Park, North Carolina).

Tests were made using 0.5, 1.0, 1.5 and 2.0%, based on dry pulp weight,of Amafast Turquoise 8GBP, a sulfonated pigment made by Ciba-GeigyCorp., Greensboro, N.C. Results of the tests are shown graphically inFIG. 1. The untreated fiber showed essentially no gain in colorintensity with increase in dye concentration. The three treated samplesshowed a relatively linear increase in intensity with increasing dyeusage. Differences between the three samples treated with the Epi-DMAcondensate are probably not statistically significant. This confirms thesurprising and unexpected results of earlier tests indicating that thebleaching treatments given to the treated pulp were not deleterious.

EXAMPLE 5

In order to determine the effect of the amount of Epi-DMA additive used,a bleached kraft market pulp, the mill sheeted product of Example 1, wasobtained and reslurried in water at 2% consistency. Sodium hydroxide wasadded to adjust pH to about 10.5. Samples were then made using 1, 2, 5and 10 kg/t Epi-DMA additive (Nalco 7655), calculated on an activematerial basis. The resulting products were dyed, using the procedure ofExample 4, with 0.5, 1.0, 1.5 and 2.0%, based on dry pulp, of PergacidBlue Black B and Pergacid Orange 5R, acid dyes also available fromCiba-Geigy. Additional sets of dyed samples were made with untreatedpulp using 10 kt/t of alum as a dye fixative. Results with the blue dyeare shown graphically in FIG. 2 and with the orange dye in FIG. 3.

Results confirmed the general trend established in the previous example,although using the present dyes all of the samples treated with theEpi-DMA condensate showed higher color intensities than those in theprevious series. The best results using alum with 2.0% dye were aboutequal to the color intensities of fiber treated with only 2 kg/tadditive and only 0.5% dye. There does not appear to be any advantage ofthe highest additive usage over the results achieved at 10 kg/t.

EXAMPLE 6

Bleached kraft pulps having 1, 2 and 5 kg/t of Epi-DMA additives,calculated on an active material basis, were used in an experiment todetermine whether the increased cationicity improved pigment retention.To this end a sodium tetrapyrophosphate dispersed rutile-type titaniumdioxide was added to a slurry of the fiber in amounts of 5, 10, 15 and20% based on the weight of dry fiber present. A slurry of 10 g dryweight fiber in 750 mL of water was refined in a high shear blender forthree minutes. Then 2 g of titanium dioxide was added and refining wascontinued for an additional minute. The slurry was further diluted withwater and handsheets were made.

An untreated control series was run as were series using 10 kg/t alumand 10 kg/t alum with 0.2 kg/t Reten 210 retention aid, a trademarked,low cationic charge density polyacrylamide product made by Hercules,Inc., Wilmington, Del.

Titanium dioxide retention of the additive treated samples, as measuredby ash content, was significantly improved over untreated pulp but wasinferior, especially at higher pigment usages, to the simple use ofalum. Untreated fiber with both alum and retention aid was markedlysuperior to any of the other treatments (FIG. 4).

Quite surprisingly, the Epi-DMA treated series fared much better whensheet opacity was compared with the amount of pigment used (FIG. 5).Opacity, as opposed to retention, is actually a much better measure ofpigment efficiency. Differences between the Epi-DMA treated fiber andthe alum or alum plus retention aid samples were relatively minor. Whenfiber treated with 4 kg/t of additive was used with a small amount ofalum (2.5 kg/t) opacity values were equal to the best obtained by anymeans for the one level of titanium dioxide tested.

EXAMPLE 7

Another series of samples was run using a crosslinked cationic additivein which a portion of the dimethylamine was replaced by hexamethylenediamine (HMDA) in the epichlorohydrin-dimethylamine condensationproduct. This product is available as Nalco N-7135 from Nalco ChemicalCo. Bleached kraft fiber was treated with 1.25, 2.5, 5 and 10 kg/t,active material basis of the additive condensate in the manner taught inExample 1. This fiber was compared with samples of fiber treated with 1,2 and 5 kg/t of the unmodified Epi-DMA condensate. Additionally, samplesof untreated pulp were used with 10 kg/t alum and 10 kg/t alum with 0.2kg/t Reten 210 retention aid.

The fiber samples were treated as described in Example 6 using 20%sodium tetrapyrophosphate dispersed titanium dioxide based on dry fiber.Retention results are shown graphically on FIG. 6 and opacity values onFIG. 7.

The HMDA modified Epi-DMA is superior to the unmodified Epi-DMAcondensate in pigment retention (FIG. 6). It is also superior to the useof alum by itself. Only the combination of alum and the cationicpolyacrylamide retention aid exceeded the treated modified condensate intitanium dioxide retention efficiency. There was little advantage seenin using more than 10 kg/t of the HMDA modified condensate.

As noted in the previous example, opacity is actually a better measureof pigment efficiency than is pigment retention. By this measure, as isseen in FIG. 7, even very low usages of the HMDA modified Epi-DMAcondensate perform in superior fashion to any of the other treatments.Again, most of the benefit appears to be gained below 10 kg/t additionrate of the condensate.

EXAMPLE 8

An additional series of samples was made in which the fiber was treatedwith 1.2, 2.5, 5 and 10 kg/t of an ethylene diamine (EDA) modifiedEpi-DMA polymer (Nalco N-8100). Titanium dioxide retention tests weremade as described in Examples 6 and 7, again using 20% TiO₂ based onfiber weight.

Pigment retention and opacity results are seen on FIGS. 6 and 7respectively. The EDA modified condensate is marginally poorer than thehexamethylene diamine (HMDA) modified condensate although it results inopacities better than those obtained with alum and a retention aid.

EXAMPLE 9

Samples were made in similar fashion to the cationic pulps described inExample 1 except that an ammonia crosslinked Epi-DMA condensate (Nalco7607) was used.

Two 20 g dry weight samples of spruce kraft pulp were added to about 750mL of water and run for 5 minutes in a high shear blender to simulaterefining. The pH was adjusted to 10.5 with NaOH. To one sample was added0.1 g of the 35% active material condensate to achieve an equivalentusage of 1.75 kg/t. Twice this amount was added to the other sample fora 3.5 kg/t equivalent usage. The treated fiber was allowed to stand for30 minutes at room temperature, drained and washed to pH 7, and madeinto handsheets.

The handsheets were sampled and 3 g dry basis of the cationic pulp wasslurried in 400 mL of water and run for 2 minutes in the high shearblender. Amafast Bond Blue dye was added equivalent to 40 kg/t of pulp.The samples were diluted to 900 mL and small handsheets made.

While colorimetric readings were not made, the dyed samples werecompared visually with a dyed untreated control sample. The higher colorintensity of the cationic fiber was immediately apparent. This wasreflected in the much lower color level of the white water of the twotreated samples as compared with the white water from the untreatedpulp.

Nitrogen contents of the samples treated with 1.75 and 3.5 kg/t of NH₃modified Epi-DMA were 0.021% and 0.025% respectively, indicating about91% and 54% retention of the polymer.

EXAMPLE 10

Trials were made to see if the cationic cellulose products of theinvention were effective in retaining anionic latices. One product wasmade as in Example 1 using 10 kg/t of Epi-DMA condensate. A secondproduct was made using 5 kg/t of the hexamethylene diamine (HMDA)modified condensate as taught in Example 7. Both usages were calculatedon an active material basis. The treated samples were slurried in waterand varying amounts of self-crosslinking acrylic emulsion latex (UCAR872, Union Carbide Corp., New York, N.Y.) were added. Handsheets werethen made from the fiber latex mixtures. In addition to the two treatedmaterials, trials were run on untreated pulp and untreated pulp withalum in ranges from 2.5 to 12.5 kg/t alum.

Untreated fiber, untreated fiber with alum and the fiber treated with 10kg/t Epi-DMA were ineffective at retaining latex which was essentiallyall lost with the white water. Fiber treated with HMDA modifiedcondensate showed excellent latex retention, as measured by increase insheet weight.

When small amounts of alum were added to the mixture of Epi-DMA treatedfiber and latex, the latex was effectively retained at alum usages of 5kg/t and greater. Alum at usages of about 2.5 kg/t also improved latexretention of fiber treated with HMDA modified polymer although not tothe same extent as with the Epi-DMA treated fiber. With the HMDAmodified sample, there did not appear to be significant advantage inusing alum in amounts greater than 2.5 kg/t.

It is apparent that the particular additive used will have some effecton the final properties of the fiber. An optimum additive for dyeretention might not be optimum for pigment retention. However, incombinations with small quantities of a supplementary cationic additive,such as alum, a synergistic effect is noted and an improved result isachieved that is not possible with either the treated fiber or thecationic additive standing by themselves.

EXAMPLE 11

The dye retention efficiency of the cationic cellulose product producedby treating a cellulosic fiber with a condensate of epichlorohydrin anddimethylamine has been demonstrated as shown in FIGS. 1-3. Similarimprovements are noted using Epi-DMA condensates modified with ammonia,ethylene diamine (EDA), and hexamethylene diamine (HMDA). These cationicfibers enable the production of papers dyed with acid dyes that haveintensities not generally achieved before the discoveries of the presentinvention. However, there is an ancillary but extremely important aspectof the invention which results from the greater efficiency of dyeutilization. That is the greatly reduced amount of dye in the whitewater resulting from papermaking. The high color intensity of this waterhas represented an extremely serious waste cleanup problem in the past.

The following examples show the effectiveness of the present cationicfiber at reducing dye in effluent. Bleached kraft fiber was treated asin Example 7 with hexamethylene diamine (HMDA) modifiedepichlorohydrin-dimethylamine condensate using 5, 10, 15, 20, 25 and 30kg/t, active material basis, of the condensate based on dry pulp. Asample of 5 g of the treated fiber was beaten in a high shear blender in1000 mL of water for 2 minutes. Amafast Bond Blue 10 GLP dye was thenadded. After the dye was dispersed, a 200 mL sample of the pulp slurrywas taken and filtered on a cellulose filter paper on a Buchner funnel.The effluent was analyzed colorimetrically using a set of knownstandards to determine dye content. Results showing the amount of dye inthe effluent white water are shown in FIG. 8. Results of a similar testseries using ethylene diamine modified Epi-DMA condensate as theadditive are given in FIG. 9.

In all cases in this example in excess of 92% of the dye was adsorbed bythe cationic cellulose product. This compares with untreated cellulosefiber run as a control in which only about 76-84% of the dye wasadsorbed. These results are remarkable since many of the dyeconcentrations used with treated fiber in this test are far greater thanwould ever be considered practical for commercial use. Typical dye usagein a paper mill to produce a deep dyed product is about 5-10 kg/t.

Since there was some adsorption of dye by the filter paper used toretain the dyed fiber, a series of tests was made using dye alone. Withdye concentrations equivalent to 5, 10 and 20 kg/t, from 91-93% of theoriginal dye was recovered in the effluent. This shows that adsorptionby the filter paper was of minor significance.

EXAMPLE 12

The following example shows the effect of pH on pickup efficiency of theEpi-DMA condensate. A series of samples was made in which bleachedspruce kraft pulp was treated with 10 kg/t, active material basis, of ahexamethylene diamine modified Epi-DMA condensate (Nalco 7135) atvarious pH levels between 7 and 10.5, according to the procedure ofExample 1. The treated fiber was drained and washed and then reslurriedin water. Pergacid Blue Black B dye (Ciba-Geigy) was added to each fibersample at a rate of 40 kg/t and handsheets were made. The followingresults were obtained.

                  TABLE III                                                       ______________________________________                                        Fiber     Color                 Cationic                                      Treatment Intensity, Kjeldahl N,                                                                              Additive                                      pH        L Value    %          Retention, %                                  ______________________________________                                        7         44.5       0.018 ± 0.006                                                                         35                                            8         41.5       --         --                                            9         42.0       --         --                                            10        38.0       --         --                                             10.5     33.8       0.058 ± 0.001                                                                         112                                           ______________________________________                                    

There appears to be an approximately linear relationship between colorintensity and treatment pH over the range studied. Because of the highlevel of condensate retained at pH 10.5, as seen by nitrogendetermination, there is little advantage seen in using a highertreatment pH.

In addition to the dyes, latices, and pigments described in the previousexamples, the cationic fibers of the present invention would be expectedto be advantageous for retention of many other papermaking additives.Included among these might be sizes, fillers, and wet strengthadditives. It will be understood by those skilled in that art thatconsideration must be given to the overall chemistry of the system andthat the cationic fibers will not necessarily perform in a superiormanner with all possible additives. It has already been seen that thereare differences in performance between the various species of Epi-DMAcondensates. While theoretical predictions can be made, much ofpapermaking remains a poorly understood art and expectations are notalways borne out by results. An example of this is the surprisingsynergism seen in latex retention when small quantities of alum are usedwith the cationic cellulose product.

EXAMPLE 13

The following example shows the performance of bleached kraft fibertreated with two types of Epi-DMA condensate and with two types of wetstrength additive. The treated products were dyed and qualitativeobservations made on color intensity.

The cationic cellulose product was made by dispersing 100 g, oven-drybasis, of a sheeted bleached kraft spruce pulp in water at 1.5%consistency using a propellor-type mixer and British disintegrator. Tosuccessive 100 g pulp batches, 0.38, 1.00 and 2.00 g of as ishexamethylene diamine modified Epi-DMA condensate (Nalco 7135, 50%solids) was added. This corresponds to as is usages of 10 and 20 kg/t. Asimilar sample was made using 115 g oven-dry equivalent of kraft fiberto which was added 1.15 g of uncrosslinked Epi-DMA condensate (Nalco7655, 50% solids material), corresponding to 10 kg/t as is usage. Thetreated fiber slurries were allowed to stand 30 minutes withoutagitation. Then the fiber was washed to a pH of approximately 7, sheetedand dried.

The above handsheets were divided into 10 g, oven-dry basis portions,reslurried in about 750 mL of water and agitated for 2 minutes in a highshear blender to simulate beating. The wet strength agent was then addedand stirred by hand for 1 minute. Finally, a solution of Amafast BondBlue 10 GLP dye was added at a 20 kg/t usage equivalent. The slurry wasagain stirred by hand for 1 minute after which handsheets were made.

Two different wet strength agents were used. The first was a highlycationic polyamine-epichlorohydrin condensate (SR-31, Monsanto Company,St. Louis, Mo.). The other was an experimental weakly cationic resin(CX-252 Nalco Chemical Co., Oak Brook, Ill.). SR-31 is sold as a 35%solids liquid and CX-252 as a 6% solids liquid. The SR-31 wet strengthagent was added to attain equivalent usages of 2.5, 5 and 10 kg/t whilethe CX-252 material was added at 2.5 and 5 kg/t, when used with the HMDAcrosslinked Epi-DMA treated fiber. Each wet strength agent was used atonly 10 kg/t when used with the unmodified Epi-DMA treated fiber.

Handsheets were tested for wet and dry tensile strengths and the ratioof the two values calculated. Higher ratios indicate better wetstrengths. Results are shown in the following tables.

                  TABLE IV                                                        ______________________________________                                        Ratio of Wet to Dry Tensile Strengths × 100                             SR-31 Wet Strength Agent                                                                     Cationic                                                                              Wet Strength                                                          Material                                                                              Agent, kg/t                                            Cationic Material                                                                              Usage, kg/t                                                                             2.5     5    10                                    ______________________________________                                        HMDA Modified Epi-DMA                                                                           5        10.49   11.86                                                                              16.52                                 HMDA Modified Epi-DMA                                                                          10        8.94    12.76                                                                              11.88                                 HMDA Modified Epi-DMA                                                                          20        10.91   12.23                                                                              --                                    Unmodified Epi-DMA                                                                             10        9.45    14.26                                                                              15.97                                 None              0        6.46     7.52                                                                              12.79                                 ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        Ratio of Wet to Dry Tensile Strengths × 100                             CX-252 Wet Strength Agent                                                                   Cationic                                                                              Wet                                                                   Material                                                                              Strength Agent, kg/t                                    Cationic Material                                                                             Usage, kg/t                                                                             2.5       5                                         ______________________________________                                        HMDA Modified Epi-DMA                                                                          5        9.45      10.33                                     HMDA Modified Epi-DMA                                                                         10        8.76      10.60 -Unmodified Epi-DMA 10 9.01 10.8                                        6                                         None             0        11.74     13.58                                     ______________________________________                                    

These results show that under the conditions of these trials, thepolyamine-epichlorohydrin wet strength agent, in combination with thecationic cellulose product, gives superior performance as compared withunmodified cellulose fiber. On the other hand, the mildly cationic wetstrength agent performed better with unmodified fiber. As a qualitativeobservation, the color intensity of the dyed sheets was inverselyrelated to the amount of wet strength agent used.

EXAMPLE 14

A sample of chlorinated Douglas-fir pulp was obtained from a pulp millbleach plant. Chlorination is the first of a five-stage bleach sequenceas outlined in Example 2. The final four stages of the sequence werecompleted in the laboratory. In this example, hexamethylene diaminemodified Epi-DMA (Nalco 7135) was added at the neutral hypochloritestage to see if it would remain on the pulp through the balance of thebleaching process. The chlorinated pulp was slurried in water and theequivalent of 2.5 kg/t NaOH added. The pH increased to 11.9. Sodiumhypochlorite solution equivalent to 15 kg/t was added. The pH of themixture dropped to 10.3. At this point, the HMDA modified Epi-DMAcondensate was added at an equivalent usage of 10 kg/t active material.The bleach was continued for 60 minutes at a temperature about 37° C.Following washing, hypochlorite, alkaline extraction and chlorinedioxide treatments were given as described previously.

Nitrogen analysis of the fully bleached pulp showed a N content of0.008%, equivalent to about 15% retention of the added condensate. It isapparent that while some of the cationic polymer is retained by thecellulose much is lost in either or both of the hypochlorite stages. Itis thus preferred to add the Epi-DMA condensate after any hypochloritetreatments and at a later alkaline stage in the bleaching sequence. Thiswould normally be the caustic extraction step in a five-stage sequenceor the hydrogen peroxide step if one is used.

The cationic nature of the product of the invention appears to bepermanent; i.e., essentially unaffected by any of the normal papermakingprocesses, many of which tend to remove the usual cationic "additives"used in papermaking.

It will be readily apparent to those skilled in the art that manyproduct variations can be made that will be considered to be within thescope of the invention. One of the principal advantages of the presentinvention is that the degree of cationicity in the product can bereadily varied. This is accomplished very simply by adjusting the amountof condensate added to the fiber. As shown in the examples, the finalproperties of the pulp will be somewhat dependent upon the particularmodification of the epichlorohydrin-dimethylamine condensate used tomodify the cellulose. It will also be evident that because of itsextreme simplicity, many process variations can be made withoutdeparting from the scope of the invention. While it is preferred thatthe condensate be added during a relatively highly alkaline stage nearthe end of the bleach sequence, this is not absolutely essential andmany variations are possible. It is further preferred that thecondensate be added later than any bleaching stage in which chlorine orsodium hypochlorite is present.

One of the major advantages of the present invention is that acid dyessuch as the tartrazine types can now be used for producing dyed paperswithout any need for retention aids. The acid dyes as a class aredesirable because their high tinctorial values would otherwise enableless dye to be used to attain a given color level. The need for alum andthe acidic conditions which it promotes is no longer necessary whenmaking a dyed product using the cationic material of the presentinvention.

Another significant advantage of the present invention is the improvedpigment retention characteristics which dictate that either no alum ormuch less alum or other retention aid is necessary for a given level ofpaper opacity. In part, this is due to the fact that the cationiccellulose of the present invention can apparently attain higher levelsof cationicity that is possible with the use of external retention aids.

Since many other features of the invention other than those disclosedabove will be apparent to those skilled in the art, the invention is tobe considered limited only as it is defined by the following claims.

What is claimed is:
 1. A method of making a cationic bleached celluloseproduct which comprises adding to an alkaline stage of a fiber bleachingsequence at least 0.5 kg/t based on the dry weight of the cellulosepresent of a cationizing agent selected from the group consisting ofcrosslinked and uncrosslinked condensates of epichlorohydrin anddimethylamine, and mixtures thereof wherein the crosslinking agent, ifpresent, is selected from the group consisting of ammonia and a primaryaliphatic diamine of the type H₂ N--R--NH₂ where R is an alkyleneradical of from 2 to 8 carbon atoms.
 2. The method of claim 1 whereinsaid bleaching sequence includes at least one hypochlorite stage and thecondensate treatment is later than the last hypochlorite stage.
 3. Themethod of claim 2 in which the bleaching sequence includes an alkalineextraction treatment following the last hypochlorite stage and thecondensate treatment is made during the alkaline extraction stage. 4.The method of claim 3 in which the alkaline extraction stage is followedby a chlorine dioxide stage.
 5. The method of claim 2 in which thebleaching sequence includes an alkaline peroxide bleaching stagefollowing the last hypochlorite stage and the condensate treatment ismade during the alkaline peroxide bleaching stage.
 6. The method ofclaim 1 in which the treatment is made with a condensate havingessentially equimolar portions of epichlorohydrin and dimethylamine. 7.The method of claim 6 in which up to 30 molar percent of thedimethylamine is replaced by ammonia.
 8. The method of claim 6 in whichup to 30 molar percent of the dimethylamine is replaced by ethylenediamine.
 9. The method of claim 6 in which up to 30 molar percent of thedimethylamine is replaced by hexamethylene diamine.
 10. The method ofclaim 1 which further comprises using the condensate in an amount 0.5-20kg/t based on the dry weight of cellulose present.
 11. The method ofclaim 10 which further comprises using the condensate in an amount of1-10 kg/t based on the dry weight of the cellulose present.
 12. Themethod of claim 1 in which the pH of the bleaching stage at which thecondensate is added is at least 9.5 or higher.